An OLED is a semiconductor device which can convert electrical energy into light energy, and is widely used in the next generation of display panels due to its advantages such as lightness, thinness, high contrast ratio, quick response and wide visual angle. Depending on its driving manner, the OLED can be an Active-Matrix Organic Light Emitting Diode (AMOLED) or a Passive-Matrix Organic Light Emitting Diode (PMOLED).
An AMOLED display device includes a plurality of pixel units arranged in a matrix, and each of the plurality of pixel units includes a red sub pixel R, a blue sub pixel B and a green sub pixel G. The red sub pixel R, the blue sub pixel B and the green sub pixel G are made of different organic light emitting materials and hence have different light emitting properties. In particular, the green sub pixel G has the strongest luminance among the red, green and blue sub pixels R, G and B, and hence imposes the most intensive stimulation to user's eyes, which directly influences the judgment made by the user's eyes on a spatial position of an image displayed in the display panel of the display device, thus resulting in a phenomenon of non-uniformity of a gravity center of a displayed image.
FIG. 1a is a structural view showing pixel units in an organic light emitting diode display device in the related art. Referring to FIG. 1a, given that areas of the red sub pixel R, the blue sub pixel B and the green sub pixel G in each pixel unit are the same to each other and the green sub pixel G has higher luminance than the red sub pixel R and the blue sub pixel B, the non-uniformity of the gravity center of a displayed image is caused when an image is displayed by the AMOLED display panel. To alleviate the non-uniformity of the gravity center of a displayed image, two green sub pixels G are provided in one pixel unit in the related art (referring to FIG. 1B). However, during manufacturing the AMOLED display panel, an alignment system with high accuracy and a Fine Metal Mask (FMM) are required to perform vapor deposition on the red sub pixel R, the blue sub pixel B and the green sub pixel G, respectively, and an offset likely happens during the vapor deposition because of the limited accuracy of the FMM, so that the organic light emitting materials are overlapped with one another to cause color mixing in the AMOLED display panel, thus decreasing the yield of the AMOLED display panel.